PSI - Issue 16

Ivan Shtoyko et al. / Procedia Structural Integrity 16 (2019) 148–152 Ivan Shtoyko, Jesús Toribio, Viktor Kharin, Myroslava Hredil / Structural Integrity Procedia 00 (2019) 000 – 000

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4

Its solution that determines the pipe residual lifetime reads: ∗ = −0,5(103 + 23 0 ) + √0,25(103 + 23 0 ) 2 + 10 5 (ℎ − 0 ) .

(7)

Fig. 2. Dependence of the pipe residual lifetime t 0 on the initial crack depth b 0 and on the initial operation time of a pipe t 0 : the curves 1 to 6 correspond to the values t 0 = 0, 4, 8, 15, 25 and 35 years, respectively . Basing on the formula (7), the graph of pipe residual lifetime ∗ dependence on the initial crack depth b 0 and the initial operation time 0 is displayed on the Figure 2. The evaluation of such crack behaviour was carried out in a time interval of 0 ≤ ≤ ∗ where ∗ = 9,76 years. As well, the series of the contours of the propagating semi elliptical crack having the initial dimensions 0 = 0,002 m and 0 = 0,001 m is shown on Figure 3 for 0 = 0 .

Fig. 3. Crack contours dependent on the residual lifetime: the curves 1 to 6 correspond to the values ∗ = 0, 2, 4, 6, 9 and 9.76 years, respectively. This way, solving the system of the differential equations with the initial and final conditions for determination of the changes of the crack semi-axes, the relation was obtained to determine the pipe residual lifetime. Based on it, the dependences of pipe residual lifetime on initial crack depth and pipe operation time were derived and it could be concluded that the pipe residual lifetime strongly depends on its initial operation time.

3. Summary

The calculation model to predict the residual lifetime of the pipe with a crack was developed considering in service degradation of the pipeline steel and the effect of soil corrosion. In this model, a crack in the pipe under the influence of the corrosion environment and gas internal pressure was considered. Based on experimental data for the studied pipeline steel, it was accepted that cracks in the steel under considered conditions propagated at constant velocity, which values were different for the non-operated pipeline steel and for the steel after 30 years of operation.